1. Field of the Invention
The present invention relates generally to surface polishing and more particularly to a method and apparatus for burnishing surface disks.
2. Description of the Prior Art
Widely used in the computer industry is a data storage medium comprised of a circular disk of flexible material up to eight inches in diameter which is coated with magnetic particles and enclosed within an envelope. These disks are known in the trade as "floppy disks." The magnetic coating is very thin and comprises minute magnetic oxide particles dispersed in a resin binder. When this coating is initially applied to the flexible material, the surface of the coating contains irregularities such as protruding particles of iron oxide or lumps of binder material. These irregularities must be removed from the coated surface before that surface can be used to record and reproduce data. Failure to remove these irregularities causes the recording-reproducing transducer to either raise slightly as it passes over such particles, reducing the quality of the recording, or to crash into the particle, ultimately destroying the oxide-coated surface.
The standard technique widely used within the industry to remove these irregularities is to polish or burnish the oxide-coated surface. U.S. Pat. No. 3,943,666 issued to Dion et al relates to disk burnishing and depicts the placing of the flexible material on a resilient surface and contacting the oxide-coated surface with a moving ceramic tool. Some deficiencies in this method have been previously pointed out as in U.S. Pat. No. 4,179,852 issued to Barnett which states that:
"The cost of the floppy dish is further increased because ceramic abrasive elements are expensive, and their useful life is quite short because the removed magnetic oxide material tends to `build up` in the ceramic abrasive material, and also wears-out the ceramic material. Further, `wipers` may in some uses be required to remove debris consisting of abraded magnetic oxide particles from the recording surface to prevent such particles from contributing to scratching of the recording layer during the continuing passing of the recording surface under the abrasive member. Such wipers add complexity and expense to the burnishing process and the burnishing machinery."
Furthermore, while the method and apparatus of the Dion reference may successfully burnish coatings whose thickness lies between 110 and 140 microinches, its use for thinner coatings, particularly those ranging between 30 and 50 microinches appears to be somewhat limited in that it tends to destroy such coatings. The inability of the Dion apparatus to burnish these thin coatings may be due to the fact that it is a slow process which generates a great deal of heat.
The Barnett patent teaches a method of burnishing floppy disks by contacting the oxide-coated surface of the recording disk with the surface of a second burnishing disk. In this method both disks rotate in the same direction in parallel planes and are positioned so a portion of the burnishing disk, not including its center, overlaps a portion of the floppy disk. The speed of rotation of the floppy disk and the burnishing disk are controlled such that the relative velocities between the burnishing disk and the floppy disk are uniform at points of contact between the two disks.